One month ago, Donald Trump publicly backed an overhaul of the nation’s air traffic control system during a White House speech, the first major policy proposal announced by the president during “Infrastructure Week.”

But standing in Trump’s way is the only Miami House Republican who voted for him during the 2016 election: Mario Diaz-Balart.

Diaz-Balart is chairman of the House subcommittee tasked with funding the Federal Aviation Administration, a powerful position that allows the veteran lawmaker to shape legislation that affects the federal budget. He’s worried that public oversight of the nation’s air-traffic control system could end if it’s run by a private non-profit controlled by various stakeholders in the airline industry.

Proponents of the plan say that privatizing the nation’s air traffic control system will lead to faster implementation of GPS technology that will result in fewer flight delays and queues on the tarmac.

Diaz-Balart bristles at calling the proposal “privatization.”

“It’s not privatization,” Diaz-Balart said. “It’s a monopoly and it will remain a monopoly as opposed to being a monopoly being run by the public sector. It will be a monopoly run by private interests with zero oversight. There’s still no competition.”

Diaz-Balart said it’s important to have elected officials in charge of overseeing the nation’s air traffic control system, because everyday citizens can choose to vote someone out of office if they think a member of Congress isn’t doing enough to rectify airplane noise or pollution complaints.

In the past, Diaz-Balart has contacted the FAA on flight paths through downtown Miami and said the FAA made changes to the flight paths after his office reached out.

That doesn’t happen if a private non-profit takes control, said Diaz-Balart, whose district includes Miami International Airport.

“Who would people go to if in fact there are issues of excess noise?” Diaz-Balart said. “Who are you going to complain to? Right now you complain to your member of Congress and we win some and lose some. I don’t have a problem with special interests but I do have a problem when you’re giving those special interests run of the U.S. airspace without competition.”

Airlines for America, a group composed of major commercial airlines in favor of privatization, said Diaz-Balart’s opposition won’t slow the bill down.

“It would be unfortunate for political turf wars in Washington to stand between the residents of South Florida and the modern, 21st century ATC system they are paying for but haven’t yet received,” Airlines for America spokesman Vaughn Jennings said in an email. “There is unprecedented momentum in favor of reforming our nation’s antiquated ATC infrastructure. We are confident that the bill will reach the floor.”

This isn’t the first time Congress has debated the merits of privatizing air traffic control. A similar bill proposed by Rep. Bill Shuster, R-Pa., never made it to the House floor last Congress after members who oversee federal spending like Diaz-Balart voiced objections.

Shuster, who is dating an Airlines for America lobbyist, was by Trump’s side during the White House speech in June. And late last month Shuster’s new bill passed the House Transportation Committee with only one Republican dissenter.

“Anyone who underestimates Bill Shuster’s ability as a legislator does so at their own peril,” Diaz-Balart said. “Bill Shuster is one of the best legislators in D.C.”

But even if Shuster’s bill makes it to the House floor and passes, there doesn’t appear to be momentum in the Senate to give Trump a legislative victory.

“The safety of the flying public should not be for sale,” Nelson said in a statement. “Handing air traffic control over to a private entity partly governed by the airlines is both a risk and liability we can’t afford to take.”

Diaz-Balart said it would be imprudent to hand over air traffic control to commercial airlines just as drones and other forms of aviation are beginning to take flight.

“I had a bunch of hearings and meetings about what the technology is right now. There’s about to be an explosion of new technology and yet this bill aims to give control to the special interests that are now using this airspace,” Diaz-Balart said. “It’s like the federal government giving control of the streets to the taxi companies… at the time when Uber and Lyft were becoming popular.”

Diaz-Balart is wary of giving away congressional oversight, much like Congress did in 2011 when the Consumer Financial Protection Bureau was created as an independent agency. Republicans have railed against the agency, first proposed by Massachusetts Sen. Elizabeth Warren, as an unaccountable bureaucracy, and Diaz-Balart said he has the same concerns about air traffic control.

Members who control federal spending and tax policy are “giving up a lot of their authority, something that is problematic both as a matter of straight politics and people desiring to hold on to what they have that gives them clout,” said Liz Mair, a Republican strategist who is opposed to the proposal.

In addition to ceding congressional oversight, Diaz-Balart is unpersuaded that turning air traffic control to a non-profit would make flying more efficient. Proponents of the plan, including Trump, have said Canada successfully implemented a similar model, but Diaz-Balart said Canada’s air traffic control system does not compare to the U.S. system.

“There’s a lot of things being thrown out there that aren’t true,” Diaz-Balart said. “Canada has 1/10th of the traffic, minimal military use and general aviation is restricted in Toronto. It took seven years for the Canadian air system to transition, seven years for a system that is 1/10th of our traffic.”

Shuster and Trump are on a tight deadline to pass the proposal soon, as Congress must also pass a 2018 budget and potential repeal of Obamacare in the coming months.

“I’m also not sure Trump has much to do with whether it passes or fails at this point,” Mair said. “I think in general Congress knows they need to do their thing, not do what the guy with the poor approval rating that seems likely to sink further wants them to do.”